Early views considered mating systems to be species-specific i.e., did not vary among different populations. As multiple populations of different species were studied, it became evident that interpopulation differences in mating systems were more common than previously imagined. In addition, use of term mating system without any modifiers was problematic since it confounded social and genetic mating systems of males and females. Therefore, I propose to conduct a comparative study to identify ecological correlates of social and genetic mating systems using prairie voles, Microtus ochrogaster. Populations of prairie voles in different parts of their range live in habitats that differ in climate, which affects the quality and distribution of vegetation. Characterization of the mating system of prairie voles has been based on a population from Illinois. If the mating system is influenced by climate and its effects on the distribution of resources, prairie voles in Kansas may display an alternative mating system. My objective is to determine whether social and genetic monogamy are seen under certain ecological conditions. The prairie vole is an interesting model system since it has been used as a model of monogamy and affiliative behavior. Understanding factors that affect variation in social mating systems (e.g. pair bonds) are key to understanding the biological basis of attachment. Eventually understanding the variability in behavioral processes involved in social mating relationships might also provide insight into the biological basis of variability in response to stressors. I will sample prairie vole populations in eastern Kansas and east-central Illinois to determine the ecological correlates of the social and genetic mating system of females and males. Animals will be live-trapped and radio tracked to determine the social mating system. Tissue samples will be collected for subsequent genetic analysis using microsatellite primers identified for prairie voles in my laboratory previously. This study will be the first to compare the social and genetic mating systems of multiple populations of a rodent thought to be monogamous, and will allow me to design experimental manipulations to determine the factors that influence mammalian mating systems.